(57) An image sensor which is capable of producing an output image superior in uniformity by correcting variations in the characteristics of solid state photosensing devices (pixels). Correction utilizes a correlation between a reset signal and sensitivity of the solid state photosensing devices, where the reset signal is produced by driving the solid state photosensing devices in a state in which no light is substantially incident. The solid state photosensing devices convert light into an electric output signal and a gain variable amplifier circuit amplifies the signal with a gain based on the reset signal. Saturation levels of the solid state photosensing devices, gains in the vicinity of the reset level, or both of them are corrected. This process removes the necessity to supply a reference signal of light in the image sensor.